Question

How do you factor the expression `b^3-4b^2-21b`?

Answer 1

b(b + 3)(b - 7)

Explanation:

`f(b) = by = b(b^2 - 4b - 21).`
`Factor y = b^2 - 4b - 21.`
Find 2 numbers knowing sum (b = -4) and product ( c = -21).
They are (3, -7).
#y = (b + 3)(b - 7)
Finally,
f(b) = b(b + 3)(b - 7)